Orthogonal Frequency Division Multiplex (OFDM) technology is employed in a Long Term Evolution (LTE) system, users are distinguished via orthogonal subcarriers, and a service cell sets multiple transmission modes, for example, whether beamforming is employed, whether Multiple Input Multiple Output (MIMO) is employed, and whether mono-user MIMO or multi-user MIMO is employed, for a UE via Radio Resource Control (RRC) signaling according to different physical-layer key technologies used and the system load, etc.
In an LTE system, a service cell independently schedules a UE, and the common process is as follows.
A UE reports information such as its location and interference environment to feed back to a network end via a measurement on a signal, where the information includes pilot signal strength of the anchor cell and the neighboring cells, a Channel Quality Indicator (CQI, i.e., a size parameter of a transmission block corresponding to the signal-to-noise ratio of a reference signal of the anchor cell that is measured, which appears in the form of an index) and Precoding Matrix Index (PMI, which is channel state information); the network side makes a scheduling decision in conjunction with the measurement information and in consideration of the Quality of Service (QoS) of a user and such criterions as cell throughput maximization, etc., and finally indicates the user to employ which time-frequency resources for transmitting data via scheduling signaling.
As different from a Code Division Multiple Access (CDMA) system, in an LTE system, there substantially exists no inter-user interference in a cell, and inter-cell interference becomes the main factor that influence the system capacity. Especially for edge users of a cell, a strong interference is laid by neighboring cells, the spectrum efficiency is low, and the performance is poor. In order to improve the performance of edge users, in an LTE system, an Inter-Cell Interference Coordinate (ICIC) technology is employed, and the inter-cell interference is reduced via static partial frequency multiplex or semi-static interference coordinate. However, for such a static and semi-static ICIC technology, the interference coordinate capability is limited; moreover, the scheduling gain of the system may be influenced, and the problem of spectrum efficiency of edge users cannot be well addressed.
In order to further improve the system performance and the edge user rate, in an LTE-Advanced system, a Coordinated multi-point transmission/reception (CoMP) technology is proposed. FIG. 1 is a schematic diagram of a multi-cell coordinated transmission solution under CoMP technology. As shown in the figure, during multi-cell coordinated transmission, a plurality of coordinated cells may simultaneously transmit data for one user (for example, CELL 1, CELL 2 and CELL 3 simultaneously transmit data for UE1, and CELL 2 and CELL 3 simultaneously transmit data for UE2), or they may transmit data for a user independently (for example, CELL 3 independently transmits data for UE3); the users may process the data of a plurality of cells in coordination, or they may independently process the data of each cell, so that the quality of a received signal may be effectively improved, or the interference may be effectively eliminated.
A plurality of cells simultaneously transmit a signal for the same user on the same time-frequency resource, and the user simultaneously receives the signals from a plurality of cells; and by employing a joint signal processing technology, the user may effectively improve the quality of valid signals and eliminate the inter-cell interference.
A UE reports information such as its location and interference environment to feed back to the network side via a measurement on a signal, hereby the network side makes a scheduling decision, and it needs to transfer the scheduling information (for example, the time-frequency resource allocated to a user) to a User Equipment (UE) in time.
In CoMP technology, it needs to schedule some UEs via multi-cell coordination; moreover, the UEs can detect signals from multiple cells in coordination. Therefore, it needs to make the corresponding network entities (including UEs, service cells and neighboring cells that take part in the coordinated transmission) know the related information of coordinated scheduling, including whether it is coordinated transmission mode or independent transmission mode, with which cells the anchor cell performs coordinated transmission, the port information of the cells that take part in coordinated transmission and information of the time-frequency resources scheduled; the defects of the prior art lie in that, the transmission modes between the LTE network and the UEs are independent, and it can only transfer the scheduling information of the anchor cell to the UE via a control channel or RRC signaling, while no timely scheduling information interaction is needed between cells, thus the requirements of CoMP cannot be met.
OFDM technology is employed in an LTE system, UEs are distinguished via orthogonal subcarriers, and substantially no inter-UE interference exists in a cell, but inter-cell interference becomes the main factor of interference, and especially for edge UEs of a cell, a strong interference is laid by neighboring cells, so that the spectrum efficiency and the performance of the UE are poor.
In order to improve system performance and edge UE performance, ICIC technology is employed in an LTE system. In this technology, inter-cell interference is reduced via static partial frequency multiplex or semi-static interference coordinate. However, for such a static and semi-static ICIC technology, the interference coordinate capability is limited; moreover, the scheduling gain of the system will be influenced, and the problem of spectrum efficiency of edge users cannot be well addressed.
In order to further improve the system performance and the edge UE performance, in an LTE-Advanced system, CoMP technology is proposed, and a distributed and independent scheduling method is proposed.
However, in such a distributed and independent scheduling method, it only provides a solution that each cell independently schedules the time-frequency resources of a UE, without providing a solution that how a plurality of cells schedule the time-frequency resources of a UE.
In conclusion, the present distributed and independent scheduling method does not provide a solution that how a plurality of cells schedule the time-frequency resources of a UE.
In a cellular mobile communication system, the interference that influences the quality of a user communication signal is derived from the communication signals of other users in the same cell and the user communication signals in neighboring cells; in an LTE system, OFDM technology is employed, different users in a cell are distinguished via orthogonal subcarriers, and the mutual interferences between different users in the same cell are reduced considerably. Therefore, in the LTE system, the interference caused by signals from neighboring cells becomes the main factor that influences the system communication quality; and especially for users located on the cell edge, because the interference caused by signals from neighboring cells is strong, the communication quality is poor.
In order to improve the communication quality of edge users of a cell, in an LTE system, inter-cell signal interference is reduced via static partial frequency multiplex or semi-static interference coordinate by employing ICIC technology. However, the anti-interference capability obtained by employing such a method is limited; moreover, the scheduling gain of the system is influenced, and the problem of poor communication quality of cell edge users cannot be well addressed.